Rolls-Royce Looking at 2017-18 Cert for Open Rotor Engine

RR expects to be able to certify its RB2011 open rotor engine in the next 9-10 years, which is a fairly aggressive schedule, when one considers the issues of noise and certification for a completely new type of engine. (paid subscription required)

In addition to noise issues, fan shrouds make conventional turbofans typically quieter, there are also issues such as bird strike and blade loss that have not been addresses from either an engineering or a regulatory perspective, and all these issues are non-trivial.